For the purposes of this application, the term optical structure includes, for example, lines, in particular horizontal lines, within an image or outlines or contours of objects within an image detected by an image recording system. Such optical structures are detected by an image recording system which is in particular installed in a vehicle. The optical structures recorded by the image recording system are used, for example, for calibrating the image recording system or for detecting the position and movement of the vehicle carrying the image recording system. Information derived from the detected optical structures may be advantageously used for the vehicle dynamics control system of the vehicle and in particular for lateral guidance as well. In motor vehicles, the use of image recording systems is intended for the detection of the vehicle surroundings. In particular, the use of image recording systems is planned in conjunction with driver assistance systems. This makes it possible, for example, to use image recording systems for automatically regulating the distance of the motor vehicle from a vehicle traveling ahead. In order to enlarge the image detection range, the use of a plurality of image recording systems in one motor vehicle is also planned, it being possible for their detection ranges to overlap at least in part. In particular, the use of stereo cameras which are made up of two image recording systems which record generally the same scene is also provided.
Methods and devices for calibrating image recording systems in motor vehicles using a calibration object are conventional. A device and a method for calibrating an image recording system using a calibration object and a position reference sensor are described, for example, in German Patent Application No. DE 102 293 36.8 A1. Furthermore, a method for calibrating an image recording system in a motor vehicle using a calibration object is described in European Application No. EP 1 120 746 A2. The calibration object is connected to the motor vehicle and is aligned in relation to the motor vehicle via a mechanical adjusting device. The calibration is performed in relation to the longitudinal axis of the motor vehicle. The longitudinal axis may be constructed by using symmetrical features on the motor vehicle, in particular, the body. Due to production tolerances, however, this longitudinal axis does not line up with the geometric driving axis, which is defined by the bisecting line of the total toe-in angle of the rear axle. The deviations between the longitudinal axis and the geometric driving axis may not be disregarded for a measuring image recording system, in particular when it is used in driver assistance systems in motor vehicles, since the geometric driving axis determines the direction of travel when driving straight ahead, independent of the position of the longitudinal axis.
Furthermore, a method for calibrating at least one image recording system which is located at and/or in and/or on a motor vehicle, using at least one calibration object is described in German Patent Application No. DE 102 46 066 A1, the image recording system generating a first unit of image information of the calibration object, preferably in the form of at least one image data record, the motor vehicle assuming a first position in relation to the calibration object, the image recording system then generating a second unit of image information of the calibration object, preferably in the form of at least one image data record, the motor vehicle assuming a second position in relation to the calibration object, the change of position of the motor vehicle from the first position in relation to the calibration object for assuming the second position being accomplished by movement of the motor vehicle, and the alignment of the image recording system in relation to the geometric driving axis of the motor vehicle being determined from at least the first and second generated units of image information of the calibration object. Also described is a device for calibrating at least one image recording system, which is located at and/or in and/or on a motor vehicle, having at least one calibration object and at least one evaluation unit, which evaluates the image information of the at least one image recording system, the evaluation unit having means which make it possible to determine the alignment of the image recording system in relation to the geometric driving axis of the motor vehicle from at least a first and a second unit of image information of the calibration object, the image information preferably being present in the form of at least one image data record. In these known systems, the calibration object is situated outside of the vehicle, in a workshop for example, making it necessary to drive there specifically for this purpose.
A method for image detection using a television camera installed in a vehicle is described in Japanese Patent No. JP 06-215134 A1. In this case, the television camera is calibrated by detecting a part of the vehicle such as an edge of the hood in particular and the image position is corrected as a function of the position of the edge of the hood. This makes it possible in principle to calibrate an image recording system using onboard systems, making it unnecessary to make a special visit to a workshop in order to perform a calibration using calibration objects present there. Modern body shapes, however, pose considerable practical problems because present-day hoods frequently no longer have distinct edges, so that calibration based on edges is no longer possible. Furthermore, high-gloss paints commonly used today result in mirror effects that make it difficult to detect body structures using an image recording system.
A method and a device for compensating a misalignment of an image generation device is described in International Application No. WO 02/50770 A1. The method includes the following steps: generating a first image using a first image generation device and storing the first image, detecting first receiving points and/or first angles of first edges and/or first lines in the first image, comparing these data obtained from the first image to corresponding data from a second image and determining correction parameters if deviations are detected, as well as using correction parameters for compensating any detected misalignment of the image generating device. However, it is difficult to implement this method for image objects without distinct edges and with strongly reflective surfaces on image objects.